Pneumatic atomizer for spraying liquids



Jan. 14, 1969 R. P. FRASER PNEUMATIC momma FOR srnume man-ms Sheet FiledSept. 25, 1964 Jan. 14, 1969 R. P. FRASER 3,421, -.'93

PNEUMATIC ATOMIZER FOR SPRAYING LIQUIDS Filed Sept. 25, 1964 Sheet 2 of4 H910 51b 37a 31a Jan. 14, 1969 R. P. FRASER 3,421,693

PNEUMATIC ATOMIZER FOR SPRAYING LIQUIDS Filed Sept. 25, 1964 Sheet 3 of4 I7 5 x 15 2 I3b j V l 11- Jan. 11, 1969 R. P. FRASER 3,421,693

PNEUMATIC ATOMIZER FOR SPRAYING LIQUIDS Filed Sept. 25, 1964 v Sheet 4of 1 United States Patent 3,421,693 PNEUMATIC ATOMIZER FOR SPRAYINGLIQUIDS Reginald Percy Fraser, Surrey, England, assignor to SocieteAnonyme de Machines Electrostatiques, Paris, France, a corporation ofFrance Filed Sept. 25, 1964, Ser. No. 399,322 Claims priority,application Great Britain, Sept. 27, 1963,

38,172/63 US. Cl. 239-15 5 Claims Int. Cl. B05b 5/02,- B05b 7/04; B05b1/26 ABSTRACT OF THE DISCLOSURE The present invention relates to apneumatic atomizer for spraying liquids, which is particularly intendedfor the spray-coating of objects with finely divided liquid particles,for example with paint.

According to the present invention, a pneumatic atomizer for sprayingliquids comprises a chamber to which a liquid to be sprayed and a gasare fed, each through a separate inlet or inlets, at such a velocity andin such a manner that they impact to at least partially atomize theliquid, and at least one outlet from the chamber through which passesthe atomized liquid particles entrained in a gas stream, and means forimparting an electrostatic charge to said particles.

The liquid and gas may be fed into the chamber as o-p posed jets orstreams, or the jets or streams may be at an angle to each other.

The chamber may be of various forms, for example cylindrical, having theliquids and gas fed through separate inlets in its side walls and havingthe outlet from the chamber at one end. Alternatively the chamber may beof annular form and provided in one of its side walls with one or moreinlets for the liquid to be sprayed and in its other side wall with oneor more inlets for the gas. Preferably a plurality of inlets, eg, forthe liquid to be sprayed, may be provided in the inner wall of theannular chamber and a number of inlets, e.g. for the gas may be providedin the outer wall of the chamber, an inlet for the gas being arrangedopposite each inlet for the liquid. Further gas inlets, not necessarilyopposed to the liquid inlets, may also be provided. It is of coursepossible to feed the gas to the inlets in the inner wall and the liquidto the inlets in the outer wall.

The outlet or ioutlets from the chamber may comprise one or moreorifices, each in the form of a narrow passage which communicatesdirectly with the chamber. Alternatively the outlet or outlets from thechamber may comprise one or more passages which lead to a furtherchamber defining or terminating in an outlet nozzle orifice.

The electrostatic charge may be applied to the particles to be sprayedby applying a high DC. potential to the chamber or alternatively byapplying this potential to the passage or passages through which theliquid to be sprayed is fed to the chamber, whereby this liquid ischarged before it enters the chamber and is atomized. Yet again thecharge maybe applied to the atomized particles after they leave thechamber.

In practice, the gas will generally be air although the "ice use ofother gases is of course within the scope of the invention.

In order that the invention may be more fully understood, reference willnow be made to the accompanying drawings, in which:

FIGURES 1 to 7 are simplified cross-sectional diagrams of differentembodiments of spraying apparatus according to this invention, and

FIGURES 8 to 13 are cross-sectional views through practical embodimentsof spraying heads according to the invention.

Referring to FIGURE 1, the spraying apparatus comprises a body 1, madeof insulating material, in which is formed a generally cylindricalchamber 2. Diametrically opposite passages 3 and 4 are provided whichprovide inlets intoopposite sides of the chamber. A gas, for example,air is fed through the passage 3 at high velocity and a liquid to besprayed, for example paint, is fed through the passage 4. The gas andliquid enter the chamber as opposed jets or streams and are impacted ormixed together, whereby the liquid is atomized and then passes out ofthe chamber entrained in a gas stream through the outlet orifice 5. Theatomized liquid particles are charged electrostatically by means of ahigh D.C. potential applied to the chamber through a conductor 6connected to the wall of the chamber opposite the outlet 5. Thispotential initially charges the thin liquid coating which forms on thewall of the chamber and then the atomized particles.

FIGURE 2 shows a further embodiment wherein the outlet 5 from thechamber 2 leads to a further chamber 7 which in turn leads to an outletorifice 8 arranged in line with the outlet 5. The further chamber 7enables further mixing of the gas and liquid and further atomization totake place. The embodiment of FIGURE 3 differs from the embodiment ofFIGURE 2. in that the outlet orifice 8 is disposed in the side wall ofthe chamber 7 at right angles to outlet 5 instead of being axiallyaligned with the outlet 5, as in the embodiment of FIGURE 2.

In the embodiment of FIGURE 4, the outlet from the chamber 2 comprises apassage 5a which meets a crosspassage 8a forming the outlet orifice.These passages meet at an intermediate point along their length and theblind end portions 512 and 8b form vibration cavities improving the:atomization of the particles.

FIGURE 5 shows a further embodiment wherein the supply passage 4 for theliquid to be sprayed is at right angles to the passage 3 feeding the gasto the chamber 2 and the outlet orifice 5 is axially aligned with thepassage 4. In addition the high voltage conductor 6 by means of whichthe electrostatic charge is applied to the liquid particles extendsthrough the passage 4.

FIGURE 6 shows an embodiment wherein the outlet from the chamber 2comprises three passages 5a, 5b, 5c, inclined at an angle to each other.The high voltage conductor 6 extends through the passage 4.

In all of the above embodiments it will be understood that more than oneinlet passage to the chamber may be provided both for the gas and forthe liquid to be sprayed.

FIGURE 7 shows an embodiment having a chamber 2a of annular form. Thepassage 4 for the liquid to be sprayed divides into two branches 4awhich enter the inner wall of the annular chamber 2a at diametricallyopposite points. Two passages 3 for the gas are provided in the outerwall of the annular chamber opposite to the passages 4 for the liquid.If desired more than two radially arranged inlets 4a for the liquid maybe provided with a corresponding number of inlets 3 for the gas arrangedopposite them. Additional gas inlets may also be provided, so that thenumber of gas inlets is greater than the number of liquid inlets. Theconductor 6 for electrostatically charging the liquid to be sprayed isconnected to the wall of the passage 4 upstream of the chamber. Aplurality of outlet passages 5 are provided from the annular chamber,and are disposed at regular intervals on a circular path so as tocommunicate with the upper wall of the chamber.

FIGURE 8 shows a practical embodiment of spray head comprising a bodyportion 10 on the upper end of which is secured a retaining cap 11 bymeans of the screwthreaded connection 12 between these two parts. Thebody portion is hollow and contains a stem 13 which has an enlarged headportion 13a whose periphery seats on a rebate 14 at the upper end of thebody portion. The enlarged head portion 13a is provided with an annularchamber 15 having four equally spaced inlet passages 16 in its innerWall for the liquid to be sprayed, and four equally spaced inletpassages 17 in its outer wall for the inlet of gas. Each passage 16 isarranged opposite to a passage 17. The passages 16 communicate with acentral bore 18 extending axially along the stem and through which theliquid to be sprayed passes. The passages 17 communicate with axiallydirected holes 19 which in turn communicate with the space 20 betweenthe interior of the body 10 and the outside of the stem 13. The gas issupplied to this space 20, and hence to the chamber 15 through the holes19 and passages 17, by means of the inlet connection 21. On top of theenlarged head portion 13:: rests a disc member 22 provided with sixequally spaced passages 23 therethrough constituting the outlet passagesfrom the annular chamber. A sealing member 24 such as an O ring may beinterposed between the disc member 22 and the outer part 13b of theenlarged head of the stem. This outer part 13b is of reduced height tofacilitate the formation-and the cleaning of the passages 17. The discmember 22 is surmounted by a nozzle member 25 provided with an outletnozzle orifice 26 in the form of a slot and containing a further chamber27 with which the outlet passages 23 communicate. The various parts areheld assembled by means of the retaining cap 11. The stem 13, discmember 22 and nozzle member 25 can be made of insulating materials orceramic. The body 10 and retaining cap 11 are also made of an insulatingmaterial.

The central bore 18 is provided with a conducting lining formed by ametal tube 28 to which the high DC. potential is applied through theWire 6 to electrostatically charge the coating material.

In operation the liquid and gas to be sprayed are fed respectivelythrough the passages 16 and 17 and are mixed, atomized andelectrostatically charged in the chamber 15 and then pass through theoutlet passages 23 into the further chamber 27 where further atomizationtakes place and from thence through the outlet nozzle slot 26 as adivergent or bats wing shape of spray.

Referring now to FIGURE 9, wherein corresponding parts bear the samereferences as in FIGURE 8, the spray head again comprises a body portion10, a retaining cap 11, and a central stem 13 having an enlarged headportion 13a in which an annular chamber 15 is formed and provided withpassages 16 and 17 respectively for the application of the liquid to besprayed and the gas to the chamber, as in the previous embodiment.However in this embodiment, instead of providing a disc member 22, anozzle member 30 is positioned on top of the enlarged head 13a of thestern, and is provided with a plurality of outlet orifices in the formof narrow passageways 31 which are inclined outwardly with respect tothe axis of the stem 13 and through which atomized liquid to be sprayedpasses directly from the annular chamber 15. Six such outlet orifices 31may be provided spaced equally from each other. Each orifice may have adiameter of about 0.022 inch and be inclined at about 19 with respect tothe longitudinal axis of the spray head. In an alternative embodiment,shown in FIGURE 10, the nozzle member 30 is provided with two rings ofoutlet orifices,

the inner ring 31a comprising three or more equally spaced holesinclined at 10 to the axis of the spray head, whilst the outer ring 31bcomprises three or more equally spaced holes inclined at 35 to the axisof the spray head. The holes may have a diameter of about 0.018 inch.

Referring now to the embodiment of FIGURE 11, wherein correspondingparts have again been given the same reference numerals as in theembodiments of FIG- URES 8 and 9, a domed nozzle member 32 is mounted ontop of the enlarged head 13a of the stem and contains an annular chamber15a which, together with the annular chamber 15 in the enlarged head 13aof the stem, forms an overall annular chamber of much greater axialextent. A plurality of inclined outlet orifices in the form of narrowpassages 33 are provided around the tip of the member 32 which projectsforwardly from the retaining cap 11 of the spray head. Sixteen suchoutlet orifices may be provided, equally spaced around the member 32,each having a diameter of about 0.02 inch and being inclined at 60 withrespect to the longitudinal axis of the spray head.

FIGURE 12 shows a further embodiment of spraying head which is ofbasically similar form to that shown in FIGURE 11 and whereincorresponding parts have the same reference numerals. In this embodimenthowever, the domed nozzle member 32 is also provided with a centralpassage 34 which has a larger diameter than the narrow passages 33. Avalve 35 with a head 37 is slidably arranged within the central bores 18and 18a through which passes the liquid to be sprayed. The end 36 ofthis valve adjacent the nozzle member 32 is tapered to form a pintle andfits within the central passage 34 to close it. The pintle valve is madeof metal and has the high DC. potential applied to it through the wire 6for the purpose of electrostatically charging the coating material.

The pintle valve is movable axially from the position shown, in whichthe passage 34 is closed by the end 36, to positions in which the pintleend 36 is withdrawn from the passage 34 and the entrance to the passageis open to some extent. The annular outlet 38 from the passage 18 closesas the pintle end 36 is withdrawn from the passage 34.

When in the position shown in the drawings in which the central passage34 is closed by the end 36 of the pintle and the outlet 38 is fullyopen, the liquid pressure in the chamber 18a is higher than the pressurein the annular chamber 15 and the device operates in the same manner asthe embodiment of FIGURE 11 to spray the liquid through the passages 33.

As the end of the pintle valve is retracted from the central passage 34to a position in which both the central passage and the annular outlet38 are open, the supply of liquid through the outlet 38 is restricted,and the air pressure in passages 19 and through holes 17 becomes greaterthan the pressure of the liquid in chamber 18a. Thus the atomised liquidceases to flow from passages 33 and atomised liquid passes from thechamber 18a around the pintle through the central passage 34 and aironly issues from the outer passages 33. The atomised liquid in thepassage 34 is electrostatically charged by the pointed end 36 of thepintle.

FIGURE 13 shows a further embodiment wherein the charging of theparticles is accomplished by a corona dis charge from an annularelectrode adjacent the passages 33. The construction is somewhat similarto the embodiment of FIGURE 12 except that the central passage 34 isomitted from the nozzle member 32 and the pintle is removed from thevalve 35. In this embodiment the stem 13 is made of metal and the nozzlemember 32 is surrounded by a metal sleeve 39, having a sharp edge 40projecting from the surface of the nozzle member and which is in contactwith the stem 13. The latter is in turn connected to a source of DC.charging potential by the wire 6 so that the liquid issuing from thepassages 33 is charged from the edge 40. The amount of liquid which ismixed with the air for spraying from the nozzle through the passages 33is controlled by the pressures and respective diameters of the liquidholes 16 and the air holes 17, and the liquid can be shut off completelyby the valve 35.

It will be appreciated that the particular number and arrangement ofpassages and outlet orifices shown in the various embodiments are givenby way of example only and that many other arrangements are possible.The number of outlet orifices and the pattern in which they are arrangedis important for determining the coverage of the outlet spray from thespray head as well as the spray pattern.

In all of the embodiments of FIGURES 8 to 13 the diameter of theenlarged head portion 13a may lie between 0.5 to 2 inches.

The volumetric proportion of the gas with respect to the liquid to besprayed may be about 60 to 1 in the final spray in the embodiments ofFIGURES 8 to 11 but can be variable in the embodiments of FIGURES l2 and13. The gas velocity fed to the mixing chamber may be between 200 and1000 feet per second and the liquid velocity of the order of 100 feetper second. The velocity of the spray issuing from the nozzle device mayalso be between 200 and 1000 feet per second depending upon therespective pressure drops to the mixing chamber and from the mixingchamber to the atmosphere. The device functions as an internal mixingatomizer and up to 90% atomization of the liquid material can occurwithin the mixing chamber or chambers. A thin liquid coating or film isformed on the wall of the chamber or chambers and on the outletorifices. This coating or film is atomized by electrostatic force at theoutlet edges of the holes or passages from which the spray emerges.

The high DC. potential may be produced by means of an electrostaticgenerator, as is manufactured by Societe Anonyme de MachinesElectrostatiques, 21 Rue Jean- Mace, Grenoble, France, for example, andmay produce an output of around 100 kilovolts.

It is however possible to achieve atomization by means of the sprayingdevices according to the invention without the use of electrostaticforce and therefore the application of a DC. potential to the spray headis not essential. i

The constructions of spray head herein described are easy to manufactureand assemble. They can also readily be disassembled for cleaningpurposes.

It will be understod that the embodiments herein described and thedimensions are only given byway of example. The ratio of the dimensionsof the outlet orifices to the dimensions of the passages entering theinternal mixing chamber or chambers are such as to produce the requiredpressure drops internally within the mixing chamber and from inside toatmosphere.

I claim:

1. In apparatus for spraying liquids, in combination, means defining asubstantially enclosed chamber having a cylindrical portion and a pairof end walls, said chamber including a plurality of oppositely disposedinlet orifices in said cylindrical portion and an outlet orifice in oneof said end walls, first conduit means for introducing liquid into saidchamber through one of said inlet orifices, second conduit means forintroducing atomizing gas under controlled velocity and pressure intosaid chamber through another of said inlet orifices, said gasinteracting with the liquid within said chamber to at least partiallyatomize said liquid during the time the liquid is in said chamber, andnozzle means communicating with the outlet orifice of said chamber forreceiving the atomized liquid particles entrained in a stream of saidgas and for discharging the same from the apparatus.

2. Apparatus for spraying liquids comprising, in combination, meansdefining a substantially enclosed chamber having a plurality of inletorifices and an outlet orifice, first conduit means for introducingliquid into said chamber through one of said inlet orifices, secondconduit means for introducing atomizing gas under controlled velocityand pressure into said chamber through another of said inlet orifices,said gas interacting with the liquid within said chamber to at leastpartially atomize said liquid during the time the liquid is in saidchamber, nozzle means communicating with the outlet orifice of saidchamber for receiving the atomized liquid particles entrained in astream of said gas and for discharging the same from the apparatus, andmeans for imparting an electrostatic charge to said liquid, said inletorifices being positioned in oppositely disposed relationship with eachother, said liquid and said gas being introduced into said chamber inthe form of opposed jets of fluid.

3. Atomizing apparatus for spraying liquids comprising, in combination,means defining a substantially enclosed annular chamber having a pair ofcylindrical side walls and a pair of end walls, said chamber including aplurality of inlet orifices respectively disposed in said side walls andan outlet orifice in one of said end walls, first conduit means forintroducing liquid into said chamber through one of said inlet orifices,second conduit means for introducing atomizing gas under controlledvelocity and pressure into said chamber through another of said inletorifices, said gas interacting with the liquid within said chamber to atleast partially atomize said liquid during the time the liquid is insaid chamber, nozzle means communicating with the outlet orifice of saidchamber for receiving the atomized liquid particles entrained in astream of said gas and for discharging the same from apparatus, andmeans for imparting an electrostatic charge to said liquid prior to itsdischarge from said nozzle means, said one inlet orifice being disposedin one of said cylindrical side walls and said another inlet orifice isdisposed in the other cylindrical side wall in opposed relationship withsaid one inlet orifice, said liquid and said gas being introduced intosaid chamber in the form of opposed jets of fluid.

4. Apparatus for spraying liquids comprising, in combination, meansdefining a substantially enclosed mixing chamber having a plurality ofinlet orifices and an outlet orifice, first conduit means forintroducing liquid into said mixing chamber through one of said inletorifices, second conduit means for introducing atomizing gas undercontrolled velocity and pressure into said mixing chamber throughanother of said inlet orifices, said gas interacting with the liquidwithin said mixing chamber to at least partially atomize said liquidduring the time the liquid is in said mixing chamber, means defining anoutlet chamber having a dischar-ge orifice, passage meansinterconnecting the outlet orifice of said mixing chamber with saidoutlet chamber for leading the atomized liquid particles thereto, saidoutlet chamber being enlarged with respect to said passage means, nozzlemeans communicating with the discharge orifice of said outlet chamberfor receiving the atomized liquid particles entrained in a stream ofsaid gas and for discharging the same from the apparatus, and means forimparting an electrostatic charge to said liquid.

5. Electrostatic apparatus for spraying liquids comprising, incombination, means including a stem member having an enlarged headportion, said head portion defining an annular chamber having aplurality of inlet orifices, plate means mounted on said head portionfor substantially enclosing said chamber, said plate means including anoutlet orifice communicating with said chamber, first conduit means forintroducing liquid into said chamber through one of said inlet orifices,second conduit means for introducing atomizing gas under controlledvelocity and pressure into said chamber through another of said inletorifices, said gas interacting with the liquid within said chamber to atleast partially atomize said liquid during the time the liquid is insaid chamber, nozzle means communicating with said outlet orifice forreceiving the atomized liquid particles entrained in a stream of saidgas and for discharging the same from the apparatus, and means forimparting an electrostatic 7 8 charge to said liquid prior to itsdischarge from said 3,131,131 4/1964 Wehner 23915 nozzle means.3,284,009 11/ 19-66 Stull et a1. 239427 References Cited v UNITED STATESPATENTS EVERETT W. KIRBY, Przmary' Exammer. 1,688,827 10/1928 Nelson239-427 5 US. Cl. X.R. 2,887,275 5/1959 Dixon et a1 239427 239-434, 5453,129,112 4/1964 Marvin 239-15

